The first year of posts was definitely lost by the time the technology was switched (SQL database) and those posts were not imported into the database. They are missing in a backup copy of the db from March 2016 and it is obvious they were never there. And if you look at the first "surviving" message, the reason is almost obvious. Bach says that an update is finished, and I now remember that the update involved storing the messages in a different folder (and perhaps also changes in the format, I am not sure about that). Whoever wrote the script to load the database was not aware of this and so the posts were not imported. That's all. No conspiracy.
I have seen the birth of bad